Simulated twelve-pole stepping motor having eight actual poles

ABSTRACT

A stepping motor having a minimum of eight stator poles formed with teeth and a rotor having teeth with the effective pitches of the teeth being different to provide a three-tooth differential between the teeth. Each stator pole has a winding, and the windings are connected into two distinct phases and energized according to a four-step sequence to simulate a twelve-pole motor to cause the rotor to move one-fourth of a rotor tooth pitch for each step of the sequence.

United States Patent [72] Inventor Albert Pllmero Wallingford, Conn. [21Appl. No. 74,416 [22] Filed Sept. 22, 1970 [45] Patented Nov. 16, 1971[73] Assignee The Superior Electric Company Bristol, Conn.

[54] SIMULATED TWELVE-POLE STEPPING MOTOR HAVING EIGHT ACTUAL POLES 9Claims, 9 Drawing Figs.

[52] U.S. CI 310/49 R, 310/163, 318/138, 318/254 [51] Int. Cl 11021:37/00 [50] Field of Search 310/46, 162,163, 49 R; 318/138, 254

[56] References Cited UNITED STATES PATENTS lie/25,445 9/1963Fredrickson 310/163 3,148,319 9/1964 Fredrickson 310/49 R 3,206,6239/1965 Snowdon 310/162 3,343,014 9/1967 Giles 310/49 R 3,428,837 2/1969Morreale et a1. 310/49 R 3,509,392 4/1970 Snowdon 310/49 R 3,510,6995/1970 Fredrickson 310/49 R 3,535,604 10/1970 Madsen et al 310/49 XPrimary Examiner-D. F. Duggan Assistant Examiner-Mark O. BuddAttorney-Johnson and Kline s EVA-[515 Lil 253 PATENTEBunv 16 I97! 3, 621,31 2

sum 1 OF 2 INVENTOR,

SIMULATED TWELVE-POLE STEPPING MOTOR HAVING EIGHT ACTUAL POLES ln U.S.Pat. No. Re. 25,445, assigned to the assignee of the present invention,there is disclosed a stepping motor having a rotor formed with 50 teethand a stator formed with either actual poles with the poles also beingformed with teeth, but with these stator teeth having a 48 pitch. Eachof the poles has a winding with the winding of four alternate polesbeing connected together to form one phase and the remaining fourintermediate pole windings being also connected together to form asecond phase. By energizing the phases according to a four-stepsequence, the rotor will advance one-fourth of a rotor tooth pitch foreach step of the sequence, which in this instance is 1.8.

The principles underlying the extent of movement for each step involvehaving the eight actual poles connected to form a four-magnetic-polerevolving field with the energization of the poles for one step of thefour-step sequence producing a 90 electrical movement of the field. Thefour steps in the sequence produce one complete cycle of the statormagnetic field and cause the poles to have for the first step in thenext sequence the same magnetic field as the first step in the priorsequence. Accordingly, the rotor requires 50 (teeth) times 4 (steps persequence) or 200 steps of l.8 to complete a revolution.

Using these principles of four actual stator poles connected to form twomagnetic poles and for each pair of magnetic poles to require a toothdifference of one tooth, to design a motor having a three-toothdifference between the stator and rotor pitches, it becomes necessary toprovide such a motor with six magnetic poles which, accordingly, wouldrequire 12 actual poles. The three-tooth difierence enables a rotorhaving a different number of teeth to be utilized and thus provide adifferent extent of movement for each step. On the other hand it is alsopossible to provide the different extent of movement while maintaining atwo-tooth difference by altering the pitch of the stator teeth.

As a specific embodiment, if it is desired to provide a stepping motorhaving 2 per step with a four-step energizing sequence, such a movementwould require a rotor having 45 teeth. If a stator having eight actualpoles is employed, it should have either 43 or 47 teeth, while if al2-actual-pole stator is used it may have 48 teeth. In the formerinstance the numberof stator teeth, when used with eight poles, rendersthe configuration of the stator teeth somewhat awkward as neither numberis easily divisible by eight, while in the latter instance, thougheasily enabling four teeth to be assigned per pole, it causes the poleto be somewhat peripherally small with a greater portionof the statoraccordingly being without teeth. Thus, in either instance, usingpresently known principles, a stator, that is substantially structurallydifierent than that presently being commercially utilized would berequired in order to obtain the desired degree of movement for eachstep.

It is accordingly an object of the present invention to provide astepping motor which utilizes a stator of presently commercial design,but by changing its manner of energization of its poles and the numberof rotor teeth, a different number of steps per revolution may beobtained, and which also may be operated by presently existing four-stepsequence stepping motor drive circuits.

Another object of the present invention is to provide a stepping motorhaving poles with windings and in which the windings are interconnectedso as to simulate a motor having a different number of poles.

A further object of the present invention is to achieve the aboveobjects with a stepping motor that may or may not have a permanentmagnet carried by a rotor and which may or may not magnetize all of itspoles simultaneously.

In carrying out the present invention, there is provided a steppingmotor which has, for one embodiment herein disclosed, a structureessentially similar to that disclosed in the above-noted reissue patent.Thus the motor has a stator formed with eight actual poles, with theperiphery of the poles being formed with teeth. Moreover, each pole hasa winding which, when energized, causes the pole to assume a magneticpolarity. A rotor is circumscribed by the stator poles and carries apermanent magnet positioned between a pair of spaced end caps with theperiphery of the end caps being formed with teeth. In another embodimentof the stepping motor that does not have a permanent magnet, the statorconstruction is the same, while the rotor has an elongated cylindricalperiphery which is formed with peripherally extending teeth. ln bothembodiments of the invention, the pitch of the teeth of the rotor isselected to provide a desired movement for each step in a four-stepstepping sequence while the stator teeth have a pitch which provides athree-tooth difference between the rotor and stator pitches.

In accordance with the permanent magnet embodiment of the invention, theeight windings of the poles are connected into a four-pole, two-phaseconfiguration while the variable reluctance embodiment (no permanentmagnet in the rotor) has four phases with there being two pole windingsper phase. In both embodiments, the interconnection of the stator polewindings is such that for each step there are at least four poles whosewindings are energized, with two of the poles being adjacent and theother two magnetized poles being spaced therefrom. A pole is consideredattracting, as herein stated, when its polarity is such as to attractthe part of the rotor that is adjacent thereto, and is considerednonattracting if its winding does notcause the pole to be magnetized orif the induced magnetic polarity is the same as that of the rotorportion opposite thereto where repulsion rather than attraction occurs.

In all embodiments of the motor, the stator field produced by the fourenergized poles of the stator is unsymmetrical in that there are threeareas of attraction with one area consisting of two adjacent poles,while the other two areas are single poles. Moreover, while the areasare not evenly positioned about the rotor, the sum of the forces causedby the, areas of attraction is essentially balanced to effect a stableposition. Each step has the same unsymmetrical areas of attraction,though with different poles, and thus the extent of movement for eachstep is the same.

Other features and advantages will hereinafter appear.

Referring to the drawings:

FIG. 1 is an elevation, partly in section, of one embodiment of a motorin which the present invention is incorporated.

FIG. 2 is a diagrammatic representation of the stator poles and rotor.

FIG. 3 is a schematic diagram showing the interconnections of thewindings for the embodiment of the motor shown in FIG. 1.

FIG. 4 is a diagrammatic representation showing the magnetic polaritiesand resulting vector magnetic field produced by energizing the windingsaccording to a fourstep sequence.

FIG. 5 is an elevation, partly in section, of another embodiment of amotor, commonly referred to as a variable reluctance type, in which thepresent invention may be incorporated.

FIG. 6 is an electrical schematic diagram of the interconnections of thewindings of the motor shown in FIG. 5.

FIG. 7 is a diagrammatic representation of the magnetic polarities ofthe stator poles and resulting vector magnetic field when the windingsin FIG. 6 are energized according to a four-step sequence.

FIG. 8 is a schematic diagram of a further embodiment of theinterconnection of the windings of the motor shown in FIG. 5.

FIG. 9 is a diagrammatic representation similar to FIG. 7 of themagnetic polarity of the poles and resulting vector magnetic fieldproduced by energizing the windings in FIG. 8 according to a four-stepsequence.

Referring to the drawing, the embodiment of the motor shown in FIG. I isgenerally indicated by the reference numeral l0 and includes a stator11, a rotor 12, and a housing 13. As shown, the stator 11 consists of astack of identical laminations 14 which are shaped to form eightidentical and equally spaced, inwardly directed poles l5-l through 15-8.

Each pole has a winding 16-1 through 16-8, respectively, associatedtherewith. Accordingly, by energization of the winding of a pole, thepole can be caused to have a selected polarity of magnetism. Moreover,the inner periphery of each of the poles is formed with stator teeth 17that are equally spaced and have in this specific embodiment a pitch of48.

The rotor 12 includes a shaft 18 supported in the housing 13 by a pairof bearings 19 and having secured thereon a permanent magnet 20. Themagnet is magnetized axially and causes one end cap 21 to have onemagnetic polarity and the other end cap 22 to have the other magneticpolarity.

Each of the end caps is fonned to have peripheral teeth 23, with theteeth being equally spaced and having in the particular embodimentherein disclosed a pitch of 45. As presently heretofore described, sucha motor is disclosed in the abovenoted reissue patent and is presentlycommercially available from the assignee, with the exception that thepitch of the rotor teeth is different.

As shown in FIG. 3, each of the windings 16 is bifilar so that eachincludes two separate portions 16-la and 16-1b as indicated for thewinding 16-1 in FIG. 3; the portion 16-1a, when energized, causes thepole -1 to be magnetized as an N pole, while the other portion l6-lb,when energized, causes the pole'lS-l to be magnetized with an Spolarity. Specifically, in FIG. 3 each portion which induces an Nmagnetic polarity in its associated pole is schematically shown by theloops of the portion extending downwardly, such as the portion l6-la isshown, while each portion that induces an S pole when energized has itsloops extend upwardly, as the portion 16-1b 16-2 so shown.

The windings are connected into four distinct phases 24a, 24a, 24b, and24b, with each phase having a portion of the windings of four poles sothat, when a phase is energized, four poles are magnetized. The phase24a when energized causes the poles 16-2 and 16-7 to be N poles and 16-3and 16-6 to be S poles. The other phases, when energized, cause thewindings in the phase to induce a magnetic polarity in their associatedpole, depending on the disposition of the loops of the windings asschematically shown in FIG. 3.

For controlling energization of the windings, there is provided a sourceof direct current, such as a battery 25 to which the phases areparallelly connected and selective energization of the phases isachieved by a switch associated with each phase.

It will be understood that the energization for the embodiment of themotor herein disclosed is a four-step sequence that is utilized in othersimilar motors and consists of energizing two phases at a time with thesequence being 24a and 24b; 24a and 24b; 24a and 24b; 24a'and 24b; 24aand 24b etc. for one direction of rotation of the rotor; while, if thesequence is reversed, then the rotor will rotate in the oppositedirection.

Shown in FIG. 4 are the polarities of the poles for each step in theabove-noted sequence. Referring to FIG. 4a, the phases 24a and 24b areenergized, which causes the poles 15-1, 15-2, 15-1, and 15-7 to be Npoles, while the other four poles are caused to be S poles. The poles15-1 and 15-2 have a similar polarity and their combined magnetic effectis vectorally shown by an arrow 26, while the magnetic effect of thepole 15-4 is shown by an arrow 27, and the magnetic effect of the pole15-7 is shown by an arrow 28. For the purpose of explanation, it will beunderstood that the herein discussion with respect to FIG. 4 refers tothe end cap 22 which is polarized by the magnet to be an S pole, andhence the teeth thereof will be attracted .to the above-noted end poles.For the end cap 21, which has an N polarity, the same attraction wouldexist, but it would only be to the S poles, 15-3, 15-5, 15-6 and 15-8.

The rotor assumes a position of least reluctance and essentially a toothof the rotor will attempt to be aligned with the stator along each ofthe arrows 26, 27 and 28. However, as the arrows 26 and 28 are separatedby l 12%", which is also true of the arrows 26 and 27, it is accordinglyimpossible for teeth to be aligned between the stator and rotor alongthe arrows 27 and 28, as the misalignment is 7%". However, a rotor toothwill essentially attempt to be aligned along the arrow 26, but actualalignment cannot occur in view of the absence of teeth between theadjacent poles 15-1 and 15-2. Moreover, it will be understood that thewindings magnetize the poles so as to produce three areas as shown bythe arrows, where the stator attracts the adjacent rotor teeth. Theareas are unsymmetrical to the extent that they are not evenly spacedfrom each other, and also that two adjacent poles which form the arrow26 produce a stronger magnetic field than the poles producing the arrows27 and 28. However, along a diametric line aligned with arrow 26, thevectoral forces are essentially balanced to provide rotationalequilibrium, and hence produce a stable position for the rotor.

In order to effect the next step in a sequence, the poles are energizedas shown in the representation FIG. 4b by energizing the phases 24a and24b. The poles 15-3 and 15-4 now form the double pole, and it hasmechanically advanced from its previous position. However, the vectormagnetic field has actually rotated counterclockwise a 30 step as thearrow 26 has moved 22 1?, the arrow 27, 225?, and the arrow 28, 45,which produces a sum of 90; but, as the vector field has three vectors,then the actual effective movement of the whole field is a 30 movementcounterclockwise.

The next step in the sequence requires the energization of the phases24a and 24b to produce the magnetic polarity of the poles shown in FIG.40. The vectors 26, 27, and 28 are also shown and it will be appreciatedthat, though the reference double pole has advanced to the poles 15-5and 15-6, the vector magnetic field has again actually only turned 30counterclockwise. Similarly, as shown in FIG. M, which indicates themagnetic polarities of the poles for the fourth step of the sequencewith phases 24a and 24b being energized, the double pole is now at thepoles 15-7 and 15-8, which effectively advances the vector magneticfield another 30 movement counterclockwise. The next step is the repeatof the polarities shown in FIG. 4a, which again produces the same changeof the double pole advancing 90, but with the vector field turning 30counterclockwise.

Thus in each of the four positions of the sequence, the rotor will be ata stable position, and this stable position changes 30 electricaldegrees for each step. However, the 30 relates to the efiective movementwhich one tooth would have, it being understood that in order to moveone complete tooth pitch, the electrical field has to move for theparticular embodiment herein described where the stator and rotor pitchdiffer by three teeth. Thus the rotor will, in a four-step sequence,produce four separate movements of identical length, with the fourmovements producing a rotational step which is the reciprocal of therotor pitch.

The direction of rotation is determined by whether the rotor has moreteeth or less teeth than the stator. In the embodiment given, with therotor having a 45 pitch and the stator having a 48 pitch, the rotor willrevolve in the opposite direction than the magnetic field is revolving,and hence will revolve clockwise. On the other hand, if the rotor pitchis 51 (more than the stator), then the rotor will revolvecounterclockwise, the same as the magnetic field.

It will be noted in FIG. 4 that each of the arrows indicated a spacedarea of magnetic attraction to the portion of the rotor oppositethereto, which has an S polarity. As in the normal construction of themotor, the other end cap 21 is indexed one-half a tooth pitch from theend cap 22 and it will have an N polarity, and hence will have threespaced areas of attraction to the four S poles shown in this figure.

It will also be understood, that, while the end caps are indexed and thestator poles are aligned, it is also possible to maintain the end capsaligned and to index the portions of the stator opposite the two endcaps one-half a tooth pitch if desired.

The present invention is also usable in a variable reluctance type motorin which the rotor does not have a permanent magnet and depends uponassuming a position of least reluctance when the poles are energized ofdifferent magnetic polarity. Referring to FIG. 5, the motor is generallyindicated by the reference numeral 30 and has a stator 31 and a rotor32. The stator is essentially the same as the stator in the previousembodiment and hence has eight poles, each of which has a winding; andfor convenience the poles and windings are given the same referencenumerals as in the prior embodiment. The only only difi'erence is thatin this embodiment each winding is formed of only one portion becauseevery pole is caused to have only one magnetic polarity. The rotorincludes a shaft 33 upon which is mounted a member 34 having a hub 35and a cylindrical periphery 36, with the periphery 36 being formed ofmagnetic material. Also, equally spaced teeth 37, which in the presentembodiment may have a pitch of 45 or 51 with the stator having a 48pitch as in the previous embodiment, are formed on the periphery 36. Fora more complete description of this motor, reference is made toapplication Ser. No. 737,191, filed June 14, 1968 now U.S. Pat. No.3,535,604, assigned to the assignee of the present invention.

Referring to FIG. 6, there is shown one manner of interconnecting thewindings 115-1 through 16-8. Thus, the windings 16-1 and 16-4 areconnected to form a first phase 37a; the windings 16-2 and 16-7 areserially connected to form phase 37b; the windings 16-5 and 16-8 areconnected to form the phase 37c; while the remaining windings 16-6 and16-3 are connected to form the phase 37d. As schematically shown by thedisposition of the loops, the windings 16-1, 16-7, 16-5, and 16-3, whenenergized, cause their respective poles to be N poles, while theremaining windings when energized induce their associated poles to be Spoles.

In use, the motor 30 is also energized according to a fourstep sequenceto cause the rotor to advance one tooth pitch by energizing of thephases 37a and 37b; 37b and 370; 37c and 37d; and 37d and 37a. In eachstep only four of the windings are energized at a time, as compared toall eight windings in the prior embodiment.

It will be noted that each phase is shown connected through switches toa battery 38 to schematically illustrate one method of energizingthewindings in the desired sequence. It will be clear, however, thatautomatic switching circuits are more effectively used, as in the priorembodiment.

As shown in FIG. 7a, the poles -1, 15-2, 15-4, and 15-7 are magnetizedfor the first step in the sequence as phases 37a and 37b are energized.As in the prior embodiment, the four magnetized poles form three spacedareas of magnetic attraction to the rotor indicated by the arrows 38, 39and 40. The arrow 38 is the result of the two adjacent poles 15-1 and15-2 being magnetized, and hence represents one area to which the rotorhas a greater magnetic attraction than the other two areas representedby the arrows 39 and 40. Moreover, as in the prior embodiment, the anglebetween the arrows 38 and 39 and 38 and 40 is l 12% whereas the anglebetween the arrows 39 and 40 is 135. As shown in FIGS. 7b, 7c, and 7d,the energization of the phases, according to the remainder of thefour-step sequence, produces a 90 rotation of the two energized adjacentpoles in a counterclockwise direction, while the vector magnetic fieldadvances 30 per step in the clockwise direction.

The rotor at each position will assume a position of least reluctancefor each step. As the forces are balanced along a diametric line throughthe arrow to the two adjacent magnetized poles, there is rotationalequilibrium providing a stable position. Also, each step has the sameextent of movement.

In the embodiment shown in FIGS. 8 and 9, the windings areinterconnected to have the two energized adjacent poles be of the samepolarity rather than of the opposite polarity as in the priorembodiment. As shown in FIG. 8, the windings 16-1, 16-2, 16-5, and 16-6are wound to induce their associated poles to be N poles when thewindings are energized, while the remaining windings induce theirassociated poles to be S poles. The same windings 16-1 and 16-4 areconnected to form phase 39a; windings 16-2 and 16-7 form phase 39b;windings 16-5 and 16-8 form phase 390; and windings 16-6 and 16-3 formphase 39d. Each of the phases is illustrated as being connected througha switch to a source of direct current 40. The winding phases areenergized in the same four-step sequence as in the prior embodiment,namely 39a and 39b; 39b and 390; 39c and 39d,- 39d and 39a; 39a and 39b,etc.

Referring to FIG. 9, for the first step where phases 39a and 391; areenergized, poles 15-1 and 15-2 are N poles, while poles 15-4 and 15-7are S poles. For the next step, when phases 39b and 39c are energizedpoles 15-7 and 15-8 are magnetized S poles, while poles 15-2 and 15-5are magnetized N as illustrated in FIG. 9b. FIGS. 91'." and 9d show themagnetization for the remaining two steps in the sequence when phases39c and 39d and 39d and 39a are energized. The areas of attraction tothe rotor are shown by arrows 41, 42 and 43, and they are identical foreach step to the corresponding step shown in FIG. 7.

In this embodiment, as in the previous embodiments, there is magneticattraction for the tooth rotor at three spaced areas, with the areasbeing unsymmetrical and with one of the areas being achieved by havingtwo adjacent poles magnetized. Moreover, the two magnetized adjacentpoles are moved electrically for each step, while the vector magneticfield moves 30 per step. The rotor in this embodiment, if it has 45teeth, which is less than the stator tooth pitch, will accordinglyrotate counterclockwise as the vector magnetic field rotates clockwise.

The path of the magnetic flux in the embodiment shown in FIGS. 6 and 7is, for FIG. 7a, from N pole 15-1 through the adjacent rotor periphery36 to S pole 15-2, and from N pole 15-7 through the adjacent rotorperiphery 36 to S pole 15-4. For the embodiment shown in FIGS. 8 and 9,for FIG. 9a, the path is from N pole 15-1 to S pole '15-7, and from Npole 15-2 to S pole 15-4 through the portions of the rotor periphery 36between the poles.

While the above-disclosed embodiments have rotors and stators which havea tooth pitch that is different, it will be understood that the presentinvention may also be utilized in stepping motors of similarconstruction wherein the pitch of the stator and rotor teeth are thesame, but in which the stator poles, rather than being equally spaced,are advanced a fraction of a tooth pitch from each other. Also, while amotor having eight poles is shown, the invention is capable of beingutilized with motors having multiples of eight poles, such as a l6- polemotor with a six-tooth difference between the stator and rotor pitches.In both instances there will be, for each eight poles, three areas ofmagnetic attraction for the rotor.

It will accordingly be appreciated that there has been disclosed astepping motor having a stator and a rotor in which both the stator androtor are formed with teeth. The stator is formed to have eight actualpoles which are interconnected in a manner which causes threeunsymmetrical spaced areas of magnetic attraction between the stator andthe rotor to occur. A rotor assumes for each energization a position ofminimum reluctance; and, as the unsymmetrical field rotates 30 for eachchange of energization to the windings, the rotor will move one-fourthof a tooth pitch for each change, thus providing for a four-stepsequence the desired movement of one rotor tooth pitch. Moreover, thoughthe magnetic field is unsymmetrical, it has rotational equilibrium andis identical for each of the steps of the sequence so that the rotormoves steps which have equal movement.

Variations and modifications may be made within the scope of the claimsand portions of the improvement may be used without others.

I claim:

1. A stepping motor comprising a stator formed with at least eightactual individual poles with the periphery of the poles being formedwith teeth and a winding associated with each pole which uponenergization effects magnetization of its associated pole; a rotorhaving a periphery formed with teeth and being positioned within thestator to have its teeth be opposite the stator teeth and means forenergizing the windings of the poles to provide an unsymmetric magneticfield having three spaced magnetic areas to which the adjacent rotorteeth are magnetically attracted.

2. The invention as defined in claim 1 in which one of the spaced areasof magnetic attraction includes two adjacent poles that are bothmagnetized to be attractive to the rotor teeth and the other two areaseach consist of a single pole with there being at least onenonattractive pole between the one area and each of the other areas.

3. The invention as defined in claim 2 in which the means for energizingincludes changing the three spaced attractive areas from a firstcondition to a second condition having three spaced attractive areas andin which the one area of two adjacent magnetized poles is located 90electrical degrees in the second condition from its location in thefirst condition.

4. The invention as defined in claim 1 in which the three spacedmagnetic areas form a vector magnetic field and in which the means forenergizing includes means for changing the energized windings to changethe areas to a different location that rotates the vector magnetic field30 from its prior location.

5. The invention as defined in claim 4 in which two of the spaced areasmove the same from their prior locations to their changed locations andthe other spaced area moves twice as far.

6. The invention as defined in claim 1 in which the rotor includes apermanent magnet and a pair of end caps having the rotor teeth fonned ontheir periphery and in which the attractecl areas for one end cap hasstator poles magnetized of one polarity and the attracted areas for theother end cap has stator poles magnetized of the opposite polarity.

7. The invention as defined in claim 1 in which the rotor includes asubstantially cylindrical member formed of paramagnetic material havingthe rotor teeth formed on its periphery and in which means for formingthe attracted areas includes energizing four poles with two poles eachhaving the same magnetic polarity.

8. The invention as defined in claim 7 in which one of the attractedareas is formed by two adjacent poles being magnetized and in which thepoles are magnetized to have the same polarity.

9. The invention as defined in claim 7 in which one of the spaced areasis formed by two adjacent poles being magnetized and in which the polesare magnetized to have the opposite polarity.

l t t 8

1. A stepping motor comprising a stator formed with at least eightactual individual poles with the periphery of the poles being formedwith teeth and a winding associated with each pole which uponenergization effects magnetization of its associated pole; a rotorhaving a periphery formed with teeth and being positioned within thestator to have its teeth be opposite the stator teeth and means forenergizing the windings of the poles to provide an unsymmetric magneticfield having three spaced magnetic areas to which the adjacent rotorteeth are magnetically attracted.
 2. The invention as defined in claim 1in which one of the spaced areas of magnetic attraction includes twoadjacent poles that are both magnetized to be attractive to the rotorteeth and the other two areas each consist of a single pole with therebeing at least one nonattractive pole between the one area and each ofthe other areas.
 3. The invention as defined in claim 2 in which themeans for energizing includes changing the three spaced attractive areasfrom a first condition to a second condition having three spacedattractive areas and in which the one area of two adjacent magnetizedpoles is located 90 electrical degrees in the second condition from itslocation in the first condition.
 4. The invention as defined in claim 1in which the three spaced magnetic areas form a vector magnetic fieldand in which the means for energizing includes means for changing theenergized windings to change the areas to a different location thatrotates the vector magnetic field 30* from its prior location.
 5. Theinvention as defined in claim 4 in which two of the spaced areas movethe same from their prior locations to their changed locations and theother spaced area moves twice as far.
 6. The invention as defined inclaim 1 in which the rotor includes a permanent magnet and a pair of endcaps having the rotor teeth formed on their periphery and in which theattracted areas for one end cap has stator poles magnetized of onepolarity and the attracted areas for the other end cap has stator polesmagnetized of the opposite polarity.
 7. The invention as defined inclaim 1 in which the rotor includes a substantially cylindrical memberformed of paramagnetic material having the rotor teeth formed on itsperiphery and in which means for forming the attracted areas includesenergizing four poles with two poles each having the same magneticpolarity.
 8. The invention as defined in claim 7 in which one of theattracted areas is formed by two adjacent poles being magnetized and inwhich the poles are magnetized to have the same polarity.
 9. Theinvention as defined in claim 7 in which one of the spaced areas isformed by two adjacent poles being magnetized and in which the poles aremagnetized to have the opposite polarity.